In a previously known solution (patent application FI A 870799), a collar at an angle of 35.degree.-40.degree. is first formed at the pipe end, then the forming cone is replaced or an auxiliary forming head is mounted on it, whereupon a final rectangular collar is formed. The cone is held by its shaft in a chuck rotatably mounted on a frame. In another known device, the forming cone can be mounted at different positions in the chuck to permit the flanging pipes of different sizes. In the known solutions, the forming cone must be fitted anew between the first and second stages of the operation, and the cone is only supported by one end. Moreover, a separate fit is needed for each pipe size.
There is also another previously known solution (FI application no. 921627), in which a conical collar is first produced and the forming element is then moved in the axial direction of the pipe away from the pipe and turned so that its forming surface is substantially perpendicular to the longitudinal axis of the pipe, whereupon a rectangular collar is formed in a manner known in itself by moving the forming element in the axial direction of the pipe towards the pipe and rotating the forming element along the edge of the pipe end. The apparatus used in this solution is provided with means for turning the forming element about its fulcrum to a first position, in which the surface of the forming element is at an acute angle to the longitudinal axis of the pipe and the forming element is supported by a first surface bearing, and to a second position, in which the surface of the forming element is substantially at right angles to the longitudinal axis of the pipe and the forming element is supported by a second surface bearing. This solution requires an operator to turn the forming cone into two different positions.
Another previously known solution is the one described in Finnish patent publication no. 73152, in which a 90.degree. collar is produced at the end of a pipe by means of a press mandrel. In this solution, the mandrel is pressed radially against the interior edge of the pipe end, requiring a large forming force and a robust mechanical structure, which increases the price of the apparatus.
Previously known is also a solution for forming a collar at the edge of a circular or elliptic metal plate, described in Swedish patent publication no. 355733. However, the device has a design that does not allow it to be used for the flanging of a pipe end.